The objective of this project is to determine the potential toxicity and carcinogenicity of isoprene, indium phosphide, gallium arsenide, and optionally glutaraldehyde, by inhalation to Fischer 344 rats and B6C3Fl mice. The basic award for each chemical includes the development of analytical chemistry and generation and monitoring methods. Once these methods have been adequately developed, toxicity/carcinogenicity studies are to be conducted. Isoprene: 104-week study is to be conducted, involving fifty animals/sex/species, at 3 exposure concentrations plus controls; in vivo genotoxicity studies in rats and mice during the first 30 days of exposure. Indium phosphide: 13-week study is to be conducted, involving ten animals/sex/species, at 5 exposure concentrations plus controls; hematology and clinical chemistry in rats, hematology in mice; in vivo genotoxicity studies in rats and mice during the first 30 days of exposure; determination of indium concentrations in whole blood, serum, testes and lung. 104-week study is to be conducted, involving fifty animals/sex/species, at 3 exposure concentrations plus controls; determination of indium concentrations in whole blood, serum, testes and lung. Gallium arsenide: 104-week study is to be conducted, involving fifty animals/sex/species, at 3 exposure concentrations plus controls; in vivo genotoxicity studies in rats and mice during the first 30 days of exposure; determination of gallium and arsenic concentrations in whole blood, serum, testes and lung. Optional study of Glutaraldehyde: 104-week study is to be conducted, involving fifty animals/sex/species, at 3 exposure concentrations plus controls.